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Jan 5, 2011 -- New research may help explain why multiple sclerosis rates have risen sharply in the U.S. and some other countries among women, while rates appear stable in men.

The study could also broaden understanding of how environmental influences alter genes to cause a wide range of diseases.

The causes of multiple sclerosis (MS) are not well understood, but experts have long suspected that environmental factors trigger the disease in people who are genetically susceptible.

In the newly published study, researchers found that women with MS were more likely than men with MS to have a specific genetic mutation that has been linked to the disease.

Women were also more likely to pass the mutation to their daughters than their sons and more likely to share the MS-susceptibility gene with more distant female family members.

Gender Influences MS Gene

If genes alone were involved, mothers would pass the MS-related gene to their sons as often as their daughters, researcher George C. Ebers, MD, of the University of Oxford in the U.K. tells WebMD.

Ebers’ research suggests that the ability of environmental factors to alter gene expression -- a relatively new field of genetic study known as epigenetics -- plays a key role in multiple sclerosis and that this role is gender-specific.

The theory is that environmental influences such as diet, smoking, stress, and even exposure to sunlight can change gene expression and this altered gene expression is passed on for a generation or two.

“The idea that the environment would change genes was once thought to be ridiculous,” Ebers says. “Now it is looking like this is a much bigger influence on disease than we ever imagined.”

The study by Ebers and colleagues included 1,055 families with more than one person with MS. Close to 7,100 genes were tested, including around 2,100 from patients with the disease.

The researchers were looking for MS-specific alterations in the major histocompatibility complex (MHC) gene region.

They found that women with MS were 1.4 times more likely than men with the disease to carry the gene variant linked to disease risk.

A total of 919 women and 302 men had the variant in the MHC region, compared to 626 women and 280 men who did not have it.

The study was published online today, and it also appears in the Jan. 18 issue of Neurology.

Genetic Alterations

Epigenetics is not evolution. Genetic alterations linked to environmental assaults can be passed down for a generation or two, but DNA usually rights itself over time, Ebers says.

“This may explain why we hardly ever see MS in families over more than three generations,” he says.

Earlier studies by Ebers and colleagues suggest that vitamin D deficiency may be the environmental stressor that triggers the MS-linked gene alterations.

Rates of the disease are highest among people living farthest from the equator, and there is widespread speculation that lack of vitamin D due to low sun exposure may explain this.

Other than Ebers’ research team, Orhun Kantarci, MD, of the Mayo Clinic in Rochester, Minn., is one of the few researches studying epigenetics as it relates to multiple sclerosis.

Kantarci calls the new research a potentially important piece of the puzzle to explain the gender difference in MS, but he adds that the research must be replicated.

“This study provides more questions than answers, but it is very interesting,” he says. “We are learning that inheritance isn’t as simple as [Gregor] Mendel described.”